You should go into the settings to see how the slots are configured.
All Apple II's prior to the IIgs and excluding the //c do not have any built in ports other than game, tape drive(which the IIgs does not have), and composite video. All other inputs and outputs were acheived through interface cards. In order to be backwards compatible with the older Apple II software, the IIgs had to map the different ports on it's back to slots.
It may be set to only try booting off of slot 5, which is what the 5.25" drives are mapped to. The 3.5" drives are mapped to slot 6.
To bring up the control panel turn the computer on, once it is on, press the key combination, [apple]+[control]+[esc]
From there it's pretty easy to figure out how to change the different settings.
Also,it is possible to change settings so you can put actual cards in the slot s instead of having them mapped to the ports on back. If you have a printer interface card installed in the IIgs, I'd try removing it, checking the settings in slots, and trying to hook up an imagewriter II or other printer that'll work with the GS to see if the built in serial ports work... as having a printer interface card could mean that the built in printer/serial port doesn't work, because it'd just be redundant otherwise.
All Apple II's prior to the IIgs and excluding the //c do not have any built in ports other than game, tape drive(which the IIgs does not have), and composite video. All other inputs and outputs were acheived through interface cards. In order to be backwards compatible with the older Apple II software, the IIgs had to map the different ports on it's back to slots.
It may be set to only try booting off of slot 5, which is what the 5.25" drives are mapped to. The 3.5" drives are mapped to slot 6.
To bring up the control panel turn the computer on, once it is on, press the key combination, [apple]+[control]+[esc]
From there it's pretty easy to figure out how to change the different settings.
Also,it is possible to change settings so you can put actual cards in the slot s instead of having them mapped to the ports on back. If you have a printer interface card installed in the IIgs, I'd try removing it, checking the settings in slots, and trying to hook up an imagewriter II or other printer that'll work with the GS to see if the built in serial ports work... as having a printer interface card could mean that the built in printer/serial port doesn't work, because it'd just be redundant otherwise.